Going well enough. I only have 4 clamps that are suitable for pressing the 1 1/2'' pine frame to the base, and, in the interest of only having to do it once, I'm gluing/securing each section of the frame to the base one at a time. This will also help me ensure that everything is lining up appropriately during the framing process, and if any small modifications need to be made to either the base or frame I'll know it now, and will be able to make those corrections as I go.
I forgot to mention:
When I took the 27'' x 35'' piece of lumber to Lowes they miscut the wood, leaving me with two pieces, neither of which would be suitable for the project. Lowes didn't have any decent unwarped birch in 4x4 sheets, so I got a 4x4 sheet of 1/4'' Oak, and had it cut into two pieces that were slightly (in the neighborhood of 1/4'' too large all around. I'll have to sand away that 1/4'' when the frame is secured.
-nihil